前端发送JSON数据node.js后端应该怎么接收啊？

Question

直接直接定义一个空串data接收数据的
function(chunk){

data += chunk

}
可现在是json数据了，昨天试了没法这样做。
然后想用可写流对象，结果总是错，下面两种方式说
events.js:160

  throw er; // Unhandled 'error' event
  ^

Error: not implemented

at Writable._write (_stream_writable.js:459:6)
at doWrite (_stream_writable.js:331:12)
at writeOrBuffer (_stream_writable.js:317:5)
at Writable.write (_stream_writable.js:243:11)
at IncomingMessage.ondata (_stream_readable.js:555:20)
at emitOne (events.js:96:13)
at IncomingMessage.emit (events.js:188:7)
at readableAddChunk (_stream_readable.js:176:18)
at IncomingMessage.Readable.push (_stream_readable.js:134:10)
at HTTPParser.parserOnBody (_http_common.js:123:22)

  var writer = new Write()

    req.pipe( writer )
    req.on("end",function () {
        console.log('数据'+ writer)
        res.writeHead(
            200,{'Content-Type':'text/plain'}
        )
        res.end( "响应数据: " + writer  )
    })

var callback = function (  ) {
  var callback = function (  ) {
        console.log('数据'+ writer)
        res.writeHead(
            200,{'Content-Type':'text/plain'}
        )
        res.end( "响应数据: " + writer  )
    }


    var writer = new Write()
    req.on('data',function (chunk) {
        writer.write(chunk , callback   )
    })

后端获取json数据应该怎么写？

Answer 1

先把响应头该成 这个 ： Content-Type':'application/json'

Answer 2

var http = require('http');
var url = require("url");
var querystring = require("querystring");
http.createServer(function (req, res) {
    req.setEncoding('utf-8');
    var postData = "";
    req.addListener("data", function (postDataChunk) {
        postData += postDataChunk;
    });
    req.addListener("end", function () {
        console.log(postData);
        var params = querystring.parse(postData);
        console.log(params);
    });
}).listen(8000, "127.0.0.1");
console.log('Server running at http://127.0.0.1:8000/');

网上找了个例子改了改，无论什么方法都是以字符串形式传递，只不过后端接收到数据后会先转化为json或是其他类型数据。于是接受数据其实都是一样的，然后通过其他方式去解析数据。
@一步 如果你说的是res.writeHead的那个地方的话，这个只是其返回的header和接受无关。